1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, facsimile apparatus, printer or the like.
2. Description of the Related Art
For this kind of image forming apparatus when a structural frame is composed of steel plate it is difficult to form a complex formation. As a result of this, often in addition to fastening together with screws or welding a plurality of steel plate parts to compose a strong structural frame, parts made of resin are further affixed as holding members to support positioning of the respective printing devices comprising the image forming apparatus. However, while in this kind of configuration a structural frame made of steel plate is advantageous in terms of strength and resistance to deformation, unfortunately, due to the large number of parts, in addition to an increase in weight, time and labor required for assembly is substantial, and manufacturing costs are increased. Moreover, due to the large number of parts, dimensional errors increase due to part combining, and in order to implement accurate positioning retention a high degree of accuracy is required for each and every part.
Conversely, composing a structural frame from resin has also been proposed. A structural frame formed from resin is lightweight and may be integrally formed in a complex formation. A structural frame of this kind is easily assembled, has few parts, and makes possible significant reductions in manufacturing costs. Moreover, as the structural frame is an integrated configuration, accurate positioning support for the respective printing devices is easily implemented. There are also examples, such as the invention disclosed in Japanese Patent Application Laid-open No. H09-222760, of monochrome image forming apparatuses in which assemblability is improved and manufacturing costs are reduced without compromising rigidity by using structural frames composed of an integrally formed resin and having a box-like shape with an open top surface.
However, resin is significantly less rigid than steel plate. In the case of color copying machines, which can obtain multi-color images, the structure for a structural frame is especially complex. As a plurality of developing devices filled with different color toners, an intermediate transfer device and the like must be embedded in the structural frame, a large space is required inside the structural frame, and this makes it extremely difficult to ensure rigidity. Furthermore, in a color copying machine, in order to clear out jammed recording medium, replace the respective printing devices and so on, a few large aperture portions are required in the structural frame for the attaching/detaching of parts. These aperture portions are not only required in the upper surface of an image forming apparatus, but also in the front, right and left surfaces, and in some cases the rear surface as well. These aperture portions are a cause of rigidity degradation in the structural frame. Moreover, as the releasing direction of a mold for resin molding used to form the structural frame is complex, the required degree of accurate positioning support becomes unobtainable.
The releasing direction of the mold for resin molding greatly influences the degree of accurate positioning support and manufacturing costs of the structural frame. It is necessary that the releasing direction of the mold be as simple as possible in order to ensure accuracy of the molded resin. Accuracy of the molded resin is easily obtained by using a mold having two simple releasing directions, as the structure of such a mold is uncomplicated. However, the shapes that can be given to parts formed using such a mold are limited. It is possible to increase the releasing directions of the mold in order to integrally form complex parts by providing a slide core, which slides inwardly and outwardly, in addition to the above-described two simple releasing directions.
However, when used for continuous molding, the complex mold for this structure requires a longer than usual cooling time. Due to the complex structure, heat from the melted resin is retained and accumulates in the seams of the mold for the slide core and soon. As a result of this, often a longer amount of time is required than that which is ordinarily sufficient for the cooling and hardening of a melted resin. Although by making part formations complex, the provision of various functions and reduction of manufacturing costs are aimed for, unfortunately, as a result of the lengthening of molding time, conversely costs are increased.
Accordingly, when an image forming apparatus structural frame is to be made from molded resin, as the degree of accuracy required is high, if the part formations are made too complex, the previously described mold also becomes complex, resulting in the required degree of accuracy being unobtainable. Moreover, to obtain these part formations the time required for molding is lengthened and manufacturing costs cannot be lowered, resulting in a problem in terms of structural frame manufacturing costs. Additionally, there is a problem from the point of view of mold manufacturing lead-time, as in order to give parts the required degree of accuracy, the time for completion of a mold of complex configuration is lengthy. Furthermore, from the viewpoint of product development this means not being able to timely supply products the market is demanding. This lengthening of the development period in order to complete a mold of complex configuration is one of the most pressing issues the manufacturing industry faces.
In terms of strength of the structural frame, in recent years, image forming apparatuses and color image forming apparatuses as well, are rapidly becoming more lightweight and compact. However, the more compact and lightweight the main body of image forming apparatuses becomes, the higher the percentage of parts in which weight fluctuates during use, such as developing devices filled with toner, as well as recording medium such as paper and so on, and the higher the percentage of the amount of fluctuation of the center of gravity during use.
When considering the lowering prices of image forming apparatuses, a low cost material having the lowest level rigidity required, such as resin, and a configuration, such as an integral formation, should be chosen as a configuration for the structural frame, which supports positioning of the respective printing devices inside the image forming apparatus. However, in the image forming apparatus, even if weight balance is taken into consideration and the respective printing devices, driving device, power supply and such are set such that weight is not locally focused, due to the above-described fluctuation of the center of gravity, weight focuses in specific positions and due to loss of balance of the reaction force added to the feet from the installation surface, the load focuses on a specific foot. As a result of this, in a structural frame of a low rigidity using resin, deformation occurs and the degree of accuracy of positioning support is reduced, causing the generation of image defects. These problems become more prominent the more compact and lightweight image forming apparatuses become.
In order to solve these kinds of problems a method for increasing the rigidity of the structural frame by increasing the thickness of the plates and such may be considered. However this kind of method cannot be employed as adverse effects such as increase in cost and weight are caused by the increase in material used.
Accordingly, when a structural frame is made of resin (to be explained later with reference to the drawings), in order to support positioning of the respective printing devices with a high degree of accuracy as previously described, usually deformation of the structural frame is prevented by integrally forming from resin only side wall portions which are mutually parallel, perpendicular to the rotational central axes of the respective printing devices and which serve as means for positioning the respective printing devices, and one connector for connecting the side wall portions, and by using a plurality of highly rigid steel plate reinforcing members to attach the side wall portions.
In this configuration if a cross section is taken of the structural frame integrally formed with resin at the rotational central axes of the respective printing devices an H-like shape is formed. Also, the releasing directions of the mold are simply a vertical direction, and a horizontal direction outward from the side wall portions. Thus it is easy to obtain the required degree of accuracy for positioning support of the respective printing devices. However this kind of configuration is problematic in that, while the structural frame is integrally formed with resin, in addition to a large number of parts, and increase in weight, time and labor required for assembly is substantial, and as a result manufacturing costs are increased.
In order to deal with this problem a complex formation can be further given to the inner wall portions by configuring a slide core in the mold, which horizontally slides inside the side wall portions. However, due to the addition of the slide core the structure of the mold becomes complex, and as a result of the heat accumulation in the mold due to continuous molding as described previously, the required degree of accuracy cannot be obtained. Moreover, if the cooling time is lengthened in order to ensure accuracy, manufacturing costs are increased. Furthermore, time for completion of a complex mold leads to a lengthening of the manufacturing lead time and also results in an inability to timely provide products the market is demanding.
Consequently, for the realization of cost lowering of the image forming apparatus itself, the configuration of the structural frame is highly problematic from the viewpoints of strength, accuracy and cost lowering.
For example, in Japanese Patent Application Laid-open No. 2004-077788, an image forming apparatus is disclosed which houses and holds processing means in between a right and a left frame of a case, for visualizing an electrostatic latent image formed on an electrostatic latent image carrier with a developer stored on a developer carrier, and transferring the developer image on the electrostatic latent image carrier onto a recording medium. The right and left frames of this image forming apparatus are formed from a resin that does not include glass fibers.
In this image forming apparatus there are apertures in three directions, and metal stays are affixed to the right and the left resin frames substantially horizontally. Due to this the frame is of a weak configuration with regard to the twisting direction. In a monochrome image forming apparatus, as layering of colors does not take place, influence of twisting of the main body frame on images is minimal. However, as in a color image forming apparatus having a tandem system layering of colors takes place, the twisting of the main body frame is problematic and directly results in color misalignment, and causes print quality to significantly deteriorate.
In Japanese Patent Application Laid-open No. 2005-77735 a frame structure is disclosed which serves as the framework of an image forming apparatus for forming images on recording material. This frame structure comprises a transport body functioning as a transport path which originates at recording material supplying means for supplying the recording material in the apparatus, and from there by way of transfer means for transferring a visual image to the recording material leads up to fixing means for fixing the visual image on the recording material onto the recording material. The frame structure further comprises a pair of side plates positioned facing either side of the transport body, a connecting member for connecting the side plates on sides facing the transport body, and a rectangular bottom plate. The frame is formed by mounting the transport body, the connecting member, and the bottom plate each at different directions on the side plates.
However, the above-mentioned method is problematic in that the number of parts of the image forming apparatus is large, and as such the cost of the mold and so on is increased. Moreover, there are problems of assembly errors which occur when mounting positioning parts of the respective units on both steel plate side plates. Furthermore, as tolerance stack-up is large, and as a transport device is connected to the frame, when removing a jam, fastening parts must be removed from the rear surface of the machine body.